Patent Documents 1 and 2 each discloses as a glass-melting furnace for melting glass raw material particles in a high temperature gas phase atmosphere and accumulating them to produce a molten glass liquid, a glass-melting furnace having a glass raw material particle feed portion and a heating means for forming a high temperature gas phase atmosphere for melting the glass raw material particles in the ceiling portion of the glass-melting furnace.
This glass-melting furnace is an apparatus for melting glass raw material particles, that are fed from the glass raw material particle feed portion into the inside of the furnace, in a high temperature gas phase atmosphere heated by a heating means, to produce liquid glass particles, accumulating the liquid glass particles in a bottom portion of the glass-melting furnace to form molten glass liquid, temporarily storing the molten glass liquid in the bottom portion of the glass-melting furnace, and discharging the molten glass liquid. Further, such a production process of molten glass is known as in-flight glass melting method. In this in-flight glass melting method, as compared with a conventional melting method using a Siemens type furnace, it is possible to reduce consumption of energy in glass-melting step to be about one thirds and to produce molten glass in a short time, and accordingly, it is possible to downsize a melting furnace, omit a regenerator, improve quality, reduce CO2 and to shorten a time for changing glass type. Such an in-flight glass melting method of glass draws attention as a technique for saving energy.
By the way, as the glass raw material particles fed from the glass-raw material particle feed portion, one comprising a mixture of glass raw materials and granulated into a particle size of at most 1 mm, is commonly employed. Each particle of the glass raw material particles fed into the glass-melting furnace is melted to be a liquid glass particle while it falls (flies) in a high temperature gas phase atmosphere, and such liquid glass particles fall downwardly and accumulate in the bottom portion of the glass-melting furnace to form a molten glass liquid. The liquid glass particles produced from the glass raw material particles may be expressed as drops of molten glass. In order to produce the liquid glass particles from the glass raw material particles in the high temperature gas phase atmosphere in a short time, the particle size of the glass raw material particles has to be small as described above. Further, usually, each liquid glass particle produced from each glass raw material particle needs to be a particle having substantially the same glass composition.
Almost all of decomposed gas components, that are generated when the glass raw material particles become liquid glass particles, are discharged to the outside of the liquid glass particles without being contained in the liquid glass particles since both of the glass raw material particles and the liquid glass particles are small particles. Accordingly, there is little risk that bubbles are formed in the molten glass liquid produced by accumulating the liquid glass particles.
Meanwhile, the glass raw material particles are particles having substantially uniform constitution, and glass compositions of liquid glass particles produced from the glass raw material particles are uniform from one another. Since the difference of glass composition among the liquid glass particles is small, there is little risk that glass composition is different between portions of molten glass liquid produced by accumulation of a large number of the liquid glass particles. Accordingly, a homogenizing means for homogenizing the glass composition in molten glass liquid, that has been required in conventional glass-melting furnaces, is scarcely required in in-flight glass melting method. Even if a small amount of liquid glass particles are different from the rest of liquid glass particles in the glass composition, since the molten glass particles are small in the particle size, a heterogeneous region of molten glass liquid, that is produced from the small amount of molten glass particles having different glass composition, is small and such a region is easily homogenized and disappears in a short time. Thus, with the in-flight glass melting method, it is possible to reduce heat energy required for homogenization of molten glass liquid and to shorten a time required for homogenization.
The glass-melting furnaces of Patent Documents 1 and 2 each has a plurality of arc electrodes and/or oxygen combustion nozzles as heating means for forming a high-temperature gas phase atmosphere, and a high-temperature gas phase atmosphere of at least 1,600° C. is formed in the furnace by a thermal plasma arc formed by the plurality of arc electrodes and/or oxygen combustion flames formed by the oxygen combustion nozzles. By feeding glass raw material particles into the high-temperature gas phase atmosphere, the glass raw material particles are changed to liquid glass particles in the high temperature gas phase atmosphere. Further, as glass raw material particles employed in Patent Document 1, ones having a particle size of at most 0.5 mm (weight-averaged) are employed for the reason that they can be changed into liquid glass particles in a short time and dissipation of generated gases is easy. Further, from the viewpoints of cost increase for reduction of the particle size of the glass raw material particles and reduction of the glass composition variation among generated liquid glass particles, ones having a particle size of at least 0.01 mm (weight-averaged) are employed.
The molten glass of about 1,600° C. produced by the glass-melting furnace of Patent Document 1 or 2 is supplied from the glass-melting furnace to a temperature conditioning tank or a refining tank, and is cooled to a temperature at which the glass is formable (about 1,000° C. in a case of soda lime glass). Then, this molten glass is supplied to a forming means of glass products such as a float bath, a fusion forming machine, a roll out forming machine, a blow forming machine or a press forming machine, and formed into glass products having various shapes. Then, the formed glass products are cooled to an approximate room temperature by an annealing means, and thereafter, subjected to a cutting step by a cutting means and/or other back-end steps as the case requires, to produce desired glass products.